BEIRUT — Syrian military helicopters dropped more improvised "barrel bombs" on the northern city of Aleppo on Sunday, a monitoring group said, bringing the death toll to at least 83 people in the latest episode of a campaign many consider a war crime.

Most of the victims killed since Friday have been civilians from the city's eastern districts, including women and children, according to the British-based Syrian Observatory for Human Rights, which has a broad network of sources across Syria.

The use of barrel bombs - oil drums or cylinders packed with explosives and metal fragments - has drawn international condemnation, including from Syria's opposition delegation and their Western backers at recent peace talks in Switzerland.

The first round of negotiations wound up on Friday without making progress towards ending Syria's three-year civil war or reducing its violence, which regularly kills more than 100 people every day.

Mohammed Al-Khatieb / AFP - Getty Images

Medical personnel look for survivors following a reported airstrike on the Tariq al-Bab district of the northern Syrian city of Aleppo on February 1, 2014.

Western powers proposed a U.N. Security Council resolution in December to express outrage at the use of barrel bombs, which they say indiscriminately target innocent civilians. The weapons have killed well over 700 people in Syria in the past six weeks.

But Russia, a staunch ally of President Bashar al-Assad, has repeatedly blocked such plans in the Security Council.

Syrian authorities say they are battling rebels controlling large portions of Aleppo, once Syria's business hub and largest city, which is now split between government and rebel forces.

The Observatory said there was "heavy congestion" at a checkpoint in a southwestern neighbourhood after the government closed it to traffic, preventing residents from fleeing the bombardment and related clashes further east.

The military also used barrel bombs in the suburbs of the capital Damascus over the weekend and carried out traditional shelling and air strikes in several other cities and villages around the country, the Observatory and other activists said.

Their reports could not be independently confirmed.

REBEL INFIGHTING

To the north of Aleppo, militants from the al Qaeda-linked Islamic State in Iraq and the Levant (ISIL) seized control of a border area with Turkey called al-Raa'i, the Observatory said.

ISIL freed more than 400 people from a prison in the area who had been held by the rival Islamist Liwa al-Tawhid unit, and clashes between the two groups continued nearby, according to the monitoring group.

In the eastern province of Deir al-Zor, ISIL also seized the Koniko Gas field from the Nusra Front and other Islamist rebels who had controlled it for several weeks after wresting it from tribal gunmen. Koniko is one of the largest gas plants in Syria.

Fighting between ISIL and rival factions seeking to push the group out of rebel-held swathes of northern and eastern Syria initially led to a rollback of ISIL dominance late last year along the border and in cities like Aleppo, Idlib and Raqqa.

But as the intra-rebel conflict has raged on, ISIL has retaken some of its bases. Both sides have lost more than 1,400 fighters in clashes and suicide car bombs.

Since March 2011, more than 130,000 people across Syria have been killed and nearly six million forced from their homes.

The conflict began with popular protests against four decades of Assad family rule but evolved into a civil war after a crackdown by security forces led to an armed uprising.